You can purchase a lot of the following: 

• 1 Allen Bradley terminal base 42LTB-5000
• 1 Allen Bradley photoswitch 42MRU-5000
• 1 Allen Bradley photoswitch 42LRC-5200
• 1 Electronics Corporation of America Photohead 42LRC-5000

Items are used and working condition is unknown, I have no way to test.  The ECA switch says "pulses when blocked". If you like  more pictures, or have any questions, please ask and be specific, I am not an expert on these.  Thank you and God Bless.